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Fix unsound optimization with explicit variant discriminants #89489

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Merged
merged 3 commits into from
Oct 4, 2021
Merged

Fix unsound optimization with explicit variant discriminants #89489

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529c353
Fix unsound optimization with explicit variant discriminants
FabianWolff Oct 3, 2021
20489ea
Update comments
FabianWolff Oct 3, 2021
dd9b476
Disable `SimplifyBranchSame` optimization for now
FabianWolff Oct 3, 2021
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26 changes: 18 additions & 8 deletions compiler/rustc_mir_transform/src/simplify_try.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -713,6 +713,8 @@ impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
ty::Adt(adt, _) if adt.is_enum() => adt,
_ => return StatementEquality::NotEqual,
};
// We need to make sure that the switch value that targets the bb with
// SetDiscriminant is the same as the variant discriminant.
let variant_discr = adt.discriminant_for_variant(self.tcx, *variant_index).val;
if variant_discr != switch_value {
trace!(
Expand Down Expand Up @@ -750,20 +752,28 @@ impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
(
StatementKind::Assign(box (_, rhs)),
StatementKind::SetDiscriminant { place, variant_index },
)
// we need to make sure that the switch value that targets the bb with SetDiscriminant (y), is the same as the variant index
if y_target_and_value.value.is_some() => {
) if y_target_and_value.value.is_some() => {
// choose basic block of x, as that has the assign
helper(rhs, place, variant_index, y_target_and_value.value.unwrap(), x_target_and_value.target)
helper(
rhs,
place,
variant_index,
y_target_and_value.value.unwrap(),
x_target_and_value.target,
)
}
(
StatementKind::SetDiscriminant { place, variant_index },
StatementKind::Assign(box (_, rhs)),
)
// we need to make sure that the switch value that targets the bb with SetDiscriminant (x), is the same as the variant index
if x_target_and_value.value.is_some() => {
) if x_target_and_value.value.is_some() => {
// choose basic block of y, as that has the assign
helper(rhs, place, variant_index, x_target_and_value.value.unwrap(), y_target_and_value.target)
helper(
rhs,
place,
variant_index,
x_target_and_value.value.unwrap(),
y_target_and_value.target,
)
}
_ => {
trace!("NO: statements `{:?}` and `{:?}` not considered equal", x, y);
Expand Down